(a) Single cell protein (SCP)

A single cell protein is a protein obtained from certain microbes, which

forms an alternate source of proteins in animal feeds. The microbes involved

in the preparation of single cell proteins are algae, yeast, or bacteria. These 

microbes are grown on an industrial scale to obtain the desired protein. For

example, Spirulina can be grown on waste materials obtained from

molasses, sewage, and animal manures. It serves as a rich supplement of

dietary nutrients such as proteins, carbohydrate, fats, minerals, and

vitamins. Similarly, micro-organisms such as Methylophilus and

methylotrophus have a large rate of biomass production. Their growth can

produce a large amount of proteins.

(b) Soil

Microbes play an important role in maintaining soil fertility. They help in

the formation of nutrient-rich humus by the process of decomposition. Many

species of bacteria and cyanobacteria have the ability to fix atmospheric

nitrogen into usable form. Rhizobium is a symbiotic bacteria found in the

root nodules of leguminous plants. Azospirillium and Azotobocter are free

living nitrogen-fixing bacteria, whereas Anabena, Nostoc, and Oscillitoria

are examples of nitrogen-fixing cyanobacteria.